1. Field of the Invention
The present invention generally relates to transport robots for transporting objects to be transported in a vacuum atmosphere.
2. Description of the Related Art
Conventionally, for vacuum apparatuses (such as, film forming apparatuses), a vacuum robot (transport robot) is used capable of transporting a substrate while a vacuum atmosphere is maintained in a vacuum chamber.
The vacuum robot transports unprocessed substrates and processed substrates in the vacuum chamber. A substrate after subjected to film forming process, for example, reaches a high temperature so that the vacuum robot is heated by transporting such a high-temperature substrate.
When the vacuum robot is heated in a vacuum, heat in the substrate is conducted through an arm of the vacuum robot, and ultimately escapes to the vacuum chamber through a base flange with which the vacuum robot is fixed to the vacuum chamber.
However, a rotary shaft for extending/shortening the arm of the vacuum robot (core shaft or inner cylinder for example) is supported by a bearing. In many cases a bearing has a spherical body, a small contact area and a very low thermal conductivity; and therefore, heat received from the substrate accumulates in the arm of the vacuum robot instead of escaping to the vacuum chamber.
In addition, the inner walls of the vacuum chamber are subjected to polishing by means of electropolishing or chemical polishing in order to suppress emitted gas. Accordingly, the inner wall surfaces of the vacuum chamber are very flat and have a significantly low radiation ratio. Consequently, the reflectivity of thermal energy at the inner wall surfaces of the vacuum chamber is significantly high, and the vacuum robot is also exposed to the thermal energy reflected on the inner wall surfaces of the vacuum chamber.
As described above, the thermal energy amount that the vacuum robot receives is large and the thermal energy amount that escapes from the vacuum robot is small. Consequently, the temperature of the vacuum robot gradually rises and reaches a very high temperature at which the thermal energy amount conducted to the vacuum robot and the thermal energy amount escaping from the vacuum robot are about the same.
Conventional vacuum robots are not suitable for use at a high temperature. In order to enable such a use at a high temperature, it is required to use a solid-lubricated bearing, which is expensive, to support a support shaft.
If the solid-lubricated bearing is not used, lubrication oil of the bearing evaporates when the vacuum robot reaches a high temperature in a vacuum. As a result, maintenance work is required at short-time intervals or an operation error occurs due to defective lubrication.
As a method for reducing the thermal energy amount that enters the vacuum robot, a method has been proposed in which a substrate and a thermal shield plate are placed on the arm in a superimposed state. However, if an energy amount carried to the outside of the vacuum environment (normally, the atmosphere environment) is small, the vacuum robot eventually reaches a high temperature.
The above-discussed related art are disclosed in Japanese Patent Laid-Open Publication No. Hei 5(1993)-74699, and Japanese Patent Laid-Open Publication No. Hei 6(1994)-204316.